Hybrid ball-roller bearing promises `the best of both`

The German bearings giant, Schaeffler, has developed a bearing with novel rolling elements said to combine the best aspects of both ball and roller technologies. The resulting "ball roller" bearings are claimed to save space, cut friction, and are about 20% thinner and lighter than conventional designs.

The new rolling elements are spherical, but have their sides cut off. They are said to offer the axial load-handling capabilities of fully spherical balls, while reducing the bearing`s width and mass. This could be used to save space, to increase load capacities and provide larger grease reservoirs, or to provide more space for better sealing.

"The idea for the ball roller came from our development engineers, who were testing ball bearings and discovered that the spherical balls tended to roll about a single axis, and made no use of those areas adjacent to this axis," explains Heinrich Hofmann, a development engineer working on special projects for Schaeffler.

A typical ball bearing uses just 70% of the ball width, so that the outer 15% on each side are redundant. The engineers experimented by removing this excess material and performed six months of advanced modelling and simulation on the new design.

"Because the balls cannot be allowed to greatly change their rotation axes, cage design was crucial," Hoffman says. "The critical conditions occur during initial rotation. Once the bearings are moving under conditions of speed and load, they become self-locating, like a bicycle wheel."

The engineers have designed a special cage so that, under load, the ball roller aligns itself as a function of the contact angle.

It is possible to fit more of the new truncated rolling elements into a given size of bearing. For example, Schaeffler has found that it can get 11 ball roller elements into a bearing that usually accommodates nine full-size balls.

Initially, Schaeffler — which owns the FAG and INA brands — is supplying the ball roller bearings as samples for potential customers to test for their applications.